Field of the Invention
The present invention relates to a method of monitoring at least one freewheel of a rotary wing aircraft. The invention also relates to a rotary wing aircraft applying the method.
The invention thus lies in the field of devices for monitoring power plants of rotary wing aircraft.
Description of Related Art
Conventionally, a rotary wing aircraft has a power plant with a rotor providing the aircraft with at least part of its lift. The rotor may also participate at least in part in propelling the aircraft. Thus, a helicopter has a main rotor that provides it both with lift and with propulsion.
The rotor is driven in rotation by a power transmission gearbox that is itself driven by at least one engine.
For example, the power plant may include a turboshaft engine having a gas generator and a free power turbine. The free turbine is then connected by a mechanical power transmission train to the power transmission gearbox.
The mechanical power transmission train is usually provided with an overrunning clutch or “freewheel”. The freewheel has a driving portion connected to an engine and a driven portion connected to the power transmission gearbox.
The function of such a freewheel is to enable the rotor to be driven by the engine while, on the contrary, preventing the engine being driven by the mechanical drive train. By way of example, the freewheel may be of particular advantage during a stage in which the rotary wing is in autorotation.
Such a freewheel may be subject to damage in the course of its use. Under such circumstances, the damaged freewheel may slip, constituting the seat of mechanical slip between two parts.
For example, the freewheel may have rollers interposed between the driving portion and the driven portion. The rollers then enable the driven portion to be driven by the driving portion. Nevertheless, the rollers can erode and no longer perform their function correctly.
On starting the engine, a worn freewheel can give rise to mechanical interruption in the mechanical drive train. If the driving portion of the freewheel no longer drives the driven portion, then a free turbine turboshaft engine runs the risk of its free turbine overspeeding. If mechanical transmission between the driving portion and the driven portion is intermittent, then the engine can be subjected to mechanical jolting in the event of the driving and driven portions suddenly engaging each other.
Slip of the freewheel can also give rise to abnormal wear of the mechanical components present between the engine and the rotor of the rotary wing, e.g. as a result of repeated jolting.
Consequently, periodic maintenance actions may be undertaken to verify the operation of each freewheel. These maintenance actions need to be carried out after flying for only a short length of time, so they are generally performed by the crew of the aircraft.
U.S. Pat. No. 3,721,325 describes a mechanism having a freewheel, but does not propose any solution for verifying its operation.
Documents EP 2 757 236, EP 2 735 508, and EP 2 518 582 are also known.
Document EP 2 757 236 describes a method of starting a turboshaft engine of an aircraft, which aircraft has a rotary wing and a freewheel interposed in a mechanical power transmission train between the engine and a rotor of the rotary wing, the engine having a gas generator and a free turbine, and the mechanical power transmission train including an upstream portion connecting the free turbine to the freewheel. In that method, the torque exerted on the upstream portion is measured with a first measurement device, and a speed of rotation of said gas generator is measured with a second measurement device. Said torque is compared with a torque threshold and said speed of rotation is compared with a speed threshold, by means of a processor unit. Starting of the engine is stopped when said torque is below the torque threshold and when said speed of rotation of the gas generator is higher than a speed threshold.